Roadside Trouble Systematic trouble shooting why the "A" will not start.

Links Anything and Everything Model A. (Maintained by Steve Plucker on the Fordbarn)

Driving tip: While driving and using an original cutout, periodically check the Ammeter to see if the system is charging. The Ammeter can be used for a quick check for the cutout. With all electrical accessories off, the Ammeter should read to the right while driving, and zero when the engine is at low idle or turned off.

The Cutout

In its simplicity a cutout is a magnetically controlled switch that provides a path for current flow from the generator to the battery. The cutout permits charging of the battery when the engine is running and prevents the battery from discharging when not.

The Coils

Inner Coil-The inner coil is made up of multiple windings of a thin wire around an iron core. The fine-wire winding is just enough to get the points to close when the generator voltage rises above 6.2V or so. Its only purpose is to create a magnetic field to pull on the armature until the contact points close. By itself the magnetic field created by the inner coil is not strong enough to keep the points closed when subject to vibrating. Once the points close, the heavy-wire (Outer Coil) begins to conduct, creating a strong magnetic field that aids the inner coil in keeping the contacts firmly closed.

Outer Coil-The outer coil is made with a heavy wire and few windings. With the points closed current from the generator travels thru the outer coil charging the battery and strengthening the magnetic field around the iron core which prevents the points from vibrating open.

The Points

Contact Points-The contact points of the cutout act as a switch and are held “Normally Open” by the armature spring. When the speed of the generator increases a magnetic field is created closing the points, thus, allowing current from the generator to flow and charge the battery.

If the generator voltage drops below battery voltage, such that the battery begins to "charge" the generator ,instead of the other way around, the current in the heavy winding will be reversed, which means it's magnetic field will work AGAINST the fine winding, and cause the points to open.

The point of "cut-in" (closure of points) is determined by the tension of the armature spring and the air gap between the iron core and contact arm. The contact points should close when the voltage of the generator has reached 6.1 to 6.3 volts. It is possible to change the "cut-in" by adjusting the air gap and/or bending the Armature Spring. (The "cut-in" charges the battery)

The point of "cut-out" (opening of points) is determined by the tension of the Armature Spring. The air gap between the contact arm and the iron core has little or no effect on the "cut-out". The cutout should occur when the ammeter reads between 0 and 2 amps. It is possible to change the "cut-out" by bending the Armature Spring, set the "cut-out" as close to 0 as possible to prevent points from arcing and burning out. (The "cut-out"stops the charging of the battery and prevents the battery from draining)

Testing Cutout On Car

Equipment:
• 3/4 Ohm Resistor
• DC voltmeter

1. Disconnect the battery wire from the Battery Terminal on the cutout
2. Install a ¾ ohm resistor to the battery terminal of the Cutout. Connect the other end of the resistor to a good ground. *
3. Start the engine and slowly increase the engine speed
4. The cutout should close between 6.1 to 6.3 volts*. Which will be evident by a sudden drop in the voltage reading.

To Adjust

1. Remove cutout from generator
2. Flip cutout over and break the two spot welds
3. Remove the cutout’s cover
4. Slight adjustments can be made by changing the air gap
5. If the voltage is less than 6.1 volts increase the springs tension by bending the bimetal downward. or increase the gap
6. If the voltage is more than 6.3 volts, decrease the voltage by bending the spring upward. or decrease the air gap.

Printable version of above assembly drawing